Implantable medical devices (e.g., expandable stents) may be designed to provide a pathway for digested material, blood, or other fluid to flow therethrough following a medical procedure. Further, some implantable medical devices may incorporate features that aid in fistula treatment, bypass procedures and/or anastomosis treatment. These medical devices may include radially or self-expanding stents which may be implanted transluminally via an endoscope. Additionally, some stents may be implanted in a variety of body lumens such as the esophageal tract, the gastrointestinal tract (including the intestine, stomach and the colon), tracheobronchial tract, urinary tract, biliary tract, vascular system, etc.
In some instances it may be desirable to design a stent which includes sufficient radial strength to maintain its positon within a body lumen while also having the ability to function as a passageway for food or other digested material to flow therethrough. However, in some stents, the compressible and flexible properties that assist in stent positioning may also result in a stent that has a tendency to migrate from its originally deployed position. For example, stents that are designed to be positioned in the esophageal or gastrointestinal tract may have a tendency to migrate due to peristalsis (i.e., the involuntary constriction and relaxation of the muscles of the esophagus, intestine, and colon which push the contents of the canal therethrough). Additionally, the generally moist and inherently lubricious environment of the esophagus, intestine, colon, etc. further contributes to a stent's tendency to migrate when deployed therein. One method to reduce stent migration may include exposing bare metal portions of the stent to the tissue of the body lumen. The stent scaffold may provide a structure that promotes tissue ingrowth into the interstices or openings thereof (e.g., the stent structure may promote a hyperplastic response). The tissue ingrowth may anchor the stent in place and reduce the risk of stent migration.
Additionally, while it is important to design stents that reduce the degree to which a stent migrates within a body lumen, it also important to design stents that may be easily removed and/or re-positioned from the body lumen post-deployment. Stents including bare portions (i.e., uncovered portions) designed to promote tissue ingrowth (e.g., to reduce stent migration as described above) may also be more difficult to remove once the tissue has anchored the stent in the body lumen. One method to reduce the force necessary to remove a stent from a body lumen may include covering a portion of the stent, thereby creating a physical barrier between the body lumen and the outer surface of the stent (e.g., reducing the surface area of the stent which may anchored via tissue ingrowth). However, covered stents may be more prone to migration than bare stents (as discussed above).
Further, in addition to designing stents capable of being both sufficiently anchored and easily removed from a body lumen, it may be desirable to design stents with features that aid digestible material in passing through a body lumen. For example, in some instances it may be desirable to design stents with an inner liner (e.g., lumen) which permits food or other digested materials to flow therethrough.
Therefore, in some instances it may be desirable to design a stent which includes both a covered portion, a non-covered (e.g., bare) portion and a tubular liner. Examples of the medical devices including covered portions, non-covered portions and inner liners are disclosed herein.